Furnace roof



April 18, 1939. R. P. HEUER FURNACE ROOF Filed May 28. i957 2sheets-sheet l 'n d' 1W 2 Sheets-Sheet 2 R. P. HEUER FURNACE RooF FiledvMay 28, 1957 April 18, 1939*.

Patented Apr. 18, 1939 TENT OFFICE f FURNACE ROOF l I -.ussel PearceHeuer, lBryn Mawr, Pa.

Application May 28, 1937, Serial No. 145,357 i 5 Claims.

The invention relates to suspended basic refractory roofs for furnacesoperating at high temperatures, particularly open hearth steel furnaceswhose roof temperatures are in excess of 2910 F. (1600 C.).

A purpose of the invention is to improve the effectiveness of ironspacers i'n a suspended basic refractory roof operating at a temperatureabove the melting point of iron.

A further purpose is to use, with iron spacers in a suspended basicrefractory roof, brick which have lower shrinkage than magnesia brick,but which are more resistant to sp-alling and more reactive with theiron spacers than vordinary chrome brick.

A further purpose is to employ individually hung furnace roof brickwhich comprise chiefly chrome ore particles Yimparting low shrinkage,

with magnesia particles bonding the chrome ore particles and renderingthem more resistant to iron oxide, and to place iron spacers laterallybetween the brick, which spacers oxidize and comsate by growth throughthe use of a matrix of.

chrome Alarger particles, to obtain rapid oxidation and prevent meltingnotwithstanding'thatthe furnace temperature is above the melting pointof iron by virtue of the thinness of the spacers and to bond the chromematrix and render it more resistant to basic oxides, and also react withthe iron oxide from the spacers to form a refractory compound by use ofmagnesia smaller particles of suitable size and in suitable proportionsas later explained.

A further purpose is to obtain a basic suspended furnace roof ofimprovedresistance to spalling, crushing, high temperatures and basic slags, andimproved volume stability. V

A further purpose is to employ oxidizable metal spacers having resilientprongs which removably grip the brick and hold the spacers to the brickduring storage, transport and assembly.

Further purposes appear in the specification and in the claims. Y

The invention relates both to the methods involved and to the apparatusemployed.

In the drawings one main form of the invention has been shown withdesirable alternate forms, choosing the main and alternate formsprimarily from the standpoints of convenience in illustration,satisfactory operation and easy demonstration of the principlesinvolved. Brick for 'suspended roofs are available in such a multitude'showing the suspended roof after it has been exposed to furnaceconditions for some time.

Figures 4 and 5 are respectively front and side elevations of one of thebricks employed in the suspended roof of Figures l to 3 inclusive.

Figure 6 is a view corresponding to Figure 1, showing a modification ofthe invention.

Figures 7 and 8 are respectively front and side elevations of thespacers employed between the adjoining rear faces of the bricks ofFigures 1 to 6 inclusiv Figure 7a is a. plan View of Figure 7, taken onthe line laf-1a.

Figures 9 and 10 are respectively front and side elevations of spacersused between the adjoining front faces of bricks in Figures 1 to 6inclusive.

Figure 9a is a plan view of Figure 9, taken on the line StL-9a;

Figures 11 and 12 are respectively front and side elevations of spacersused between adjoining side faces of the bricks in Figures 1 to 6inclusive.

Figure 11a is a top plan view of Figure 11.

Figure 13 is a front elevation of an alternate form of brick, showing aside spacer to be used with the alternate form.

Figure 14 is a fragmentary section of Figure 13 on the line I4-I4,showing a front spacer employed in connection with the brick of Figures13" and 14.

In the drawings similar numerals refer to corresponding parts.

In referring to the unit used in constructing a suspended roof as abrick, it is desired, of course, to include any block or similar shape,the word brick being employed as a convenient generic term Yto cover anypreformed refractory shape, regardless of whether it is preliminarilyred or is subjected to furnace temperature for the first time in thefurnace roof.'

'I'he present inventor has previously proposed the construction of basicsuspended refractory roofs from individually hung chrome or magnesiabrick laterally spaced by spacers of iron or some In accordance withthis prior proposal of the -high shrinkage.

present inventor, when the roof is subjected to furnace temperature, themetallic spacers oxidize particularly at the ends toward the furnace,and, since vthe oxide occupies greater volume than the original metal ofthe spacer, the spacers swell or grow, filling any moderate spaces leftbetween the brick at the time the roof is constructed and vcompensatingfor shrinkage which occurs in the brick when it is heated up to furnacetemperature. The compensation for shrinkage by growth of the spacer hasbeen of' primary importance where roof brick are unflred previous tobeing subjected to furnace temperature because the inevitable shrinkagein such unred brick is greater than that exhibited by similarbricktwhich have been prellminarily fired. y

As a result of experiments upon the brick of the prior invention, it hasbeen discovered that certain difllculties which may be encountered inbasic suspended refractory roofs may be overcome and improvements insuch roofs may be made by departing in certain respects from the priorpractice. Particularly where basic suspended refractory roofs are beingemployed in high temperature furnaces such as open hearth steel furnaceswhere the roof temperature (on the side toward .the interior of thefurnace) is above the melting point of'iron, there is considerabledanger that the spacers, suitably made of iron, will melt out beforethey oxidize and therefore fail to perform their function of filling thespace between adjoining bricks and bonding the bricks together.Especially where vthe unflred brick of the prior art have been used, theinevitable shrinkage of the brick is so great that the spacers mustnecessarily be quite thick in order to be able to compensate for theshrinkage by lgrowth The relatively great thickness of the spacer, whilefavorable from the standpoint of compensating for shrinkage of thebrick, is distinctly unfavorable from the standpoint of avoiding meltingof the spacer, as an unduly thick spacer, even when it oxidizes at thesurface, still has a metallic core which is likely to melt.

Where the major constituent of the brick is magnesia, a relatively highshrinkage is inevitable at temperatures such as those attained by ltheopen hearth steel furnace, and relatively thick spacers are needed tocompensate for the However, such relatively thick spacers do notfunction satisfactorily at the open hearth steel furnace temperaturebecause they melt out between the brick. l

Brick whose chiefv constituent is chrome ore have desirably lowshrinkage at the open hearth steel furnace temperature, but in prior artpractice have often been objectionable from the standpoint of lowresistance to spalllng and to basic oxides and failure to unite flrmlyin all cases with the oxidizedfspacer. The fact as developed by theexperiments of the present inventor would seem to be that magnesiachemically combines readily'with the iron oxide of the spacer,'form inga compound, p oibly magnesium ferrite,

' which is quite refractoryv andvery strong and volume stable, whereaschrome, on the other hand, chemically unites with the iron ox'ide muchless readily and does not appear to produce a union of as great strengthas that formed with magnesia.

In accordance with the present invention, it is proposed to employ asuspendedA furnace roof bility equal to or superior to that of chromebrick,

thus making'it possible to employ thin spacers, the spacer thicknessbeing preferably not greater than 3/,4ths of an inch (0.109 centimeter).In resistance to spalling and to basic oxides, the brick employed in thepresent invention is superior to prior art chrome brick. Due apparentlyto its magnesia content, the brick of the present )invention has theproperty .of chemically combining readily with the oxidized spacer, in avery desirable manner to form the adjoining brick into a monolithicmass.

In this way it is possible to 'produce a suspended roof which issatisfactory for furnaces operating at Very high temperatures, such asopen hearth steel furnaces in which the temperature is in excess of 2910F. (1600 C.). The spacer does not melt out objectionably under openhearth steel furnace conditionsl apparently because, dueA to itsthinness, it oxidizes very quickly and combines with the refractory. Dueto the small brick shrinkage, the growth of the thin spacer issuiilcient to fill the spaces left during construction and to compensatefor the shrinkage. The brick are inherently` very resistant to spalling,and

spalling is further reduced by the chemical combination between the ironoxide of the spacer and the magnesia of the brick, which holds spalledfragments in place in the roof.

In order to facilitate construction of the roof, the spacers are verydeslrably provided with resilient prongs by which the plates can besecured to the brick before assembling the'roof. One of the prongs maybe the flange whichha's heretoforebeen used to prevent the spacer fromdrop-A ping out of its position between the bricks. A cooperating prongdesirably has contact with the hot face of the brick. After the furnaceis -brought up to temperature, the prongs exposed at the hot face willof course melt off, but by that time they will have performed theirfunction. In conventional suspended roof constructions, the bricks hangwith the longest dimension4 generally vertical, exposing the smallest face to the furnace interior. The bricks arepreferably indi-l viduallyhung from hangers, although of course they may if desired be hung insmall groups. in which case one or more bricks of each group may besupported from other bricks. This generally vused suspended roofconstruction may be employed in the present invention.

Where the roof is to be subjected to very high temperatures, such asthose of the open hearth steel furnace, the spacers which are placedbetween some or preferably all of the adjoining lateral faces of thebricks will be of iron. The designation iron is intended to includealloys in which iron is the predominant constituent, such as steel. Infurnaces operating at substantially lower temperatures than that of theopen hearth steel furnace,\spacers of copper or aluminum may be used,but it will be. understood that iron is the preferable material for thespacers even under lower temperature conditions.

The spacers should be sheet metal of a thickness preferably not greaterthan 3yaths of an inch (0.109 l centimeter), the desirable spacerthickness being 15nd of an inch (0.079A centimeters). vEach spacershould preferably be a single sheet in thickness, and, if, the spacer inthickness comprises two or more sheets, it should not be hollow. Thecumulative effect of the oxidation and corresponding growth of thespacers is to press the bricks firmly against one another in a lateraldirection, and this tightness of interiitting between the lateral facesof the bricks will increase as more and more of each spacer .oxidizes,although in many instances the spacers will not oxidize all the way tothe cold face of the bricks.

It will of course be understood that the present invention is notapplicable to acid (silica) bricks, since these would flux the ironoxide of the spacer and destroy the roof.

Figures 1 and 2 show a typical fragment of a suspended roof structure ofthe present invention as it will appear after construction and l beforethe furnace has been heated. The bricks 2U have front faces 2|, rearfaces 22, side faces 23, cold or top faces 24 and hot or bottom faces 25directed toward the interior 'of the furnace.

The brick are individually suspended by hangers 26 engaging in recess 21in the brick. The hangers are supported from any conventional overheadstructure (suggested by hooks 26') on any suitable side structure, notshown. The hangers may if desired be supported in groups so that aparticular section of the roof can be removed as a unit. If this is tobe done, it may be advisable to omit spacers at the line of junctionbetween the roof units, so that lateral interlocking will not take placeto prevent removal of the brick units.

In the form of Figures 1 and 2, each hanger 26 has twoprojections 28 and29 which extend in opposite directions, and each of which supports anindividual brick. The projections 28 and 29 engage the downwardlydirected surfaces 30 of the recess 27 while the vupwardly directedsurfaces 3l of the recesses slope to provide clearance for, and permitready insertion of, the projections 28 and 29. Each of the bricks is cutout at 32 to pass the body 33 of one of the hangers 26. The hangers 26and the cooperating recesses in the bricks are conventional means forsupporting a suspended roof.

If desired, the suspended roof may be sur- -rounded by a permanent framestructure 34, of

which part only is shown. Such a structure,

where used, confines the brick of the roof later- I ally and exertslateral pressure against adjoining brick in the roof. The framestructure 34 as shown consists of I-beams 35 and 36 joined b y a strip3l fastened at 38 to the respective I-beams. The lateral supports may beeliminated if desired, and are not present in Figure 6. A lateral thruston the brick can be obtained by permanent expansion of the spacerswithout the use of .lateral supports, due to the tendency of the bricktoremain in vertical position under the action of gravity and due to thetendency of the hangers to remain in vertical position.

The spacers 39 are preferably o-f three types, which t the peculiarities'in shape of the respective faces of the brick. Each ofthe spacers has aange '40, adapted to rest upon the upper face 24 of avbrick as at 4I andthus prevent the spacer from dropping out of its position between thebricks before oxidation occurs to hold the spacer in place. At theirends, the flanges 43 are desirably mitered as shown at 42 to prevent thenecessity of having one iiange overlap another flange at a corner of thebrick.

In order to prevent handling the spacers separately from the bricks atthe time of assembly, the spacers are desirably secured to the bricks,

as by suitable prongs. The flange may be used to function as a prong atone end, while a cooperating prong 43 is placed at the opposite end ofthe spacer to engage the lower face 25 of the brick. The sheet ironcomposing the spacer is somewhat resilient so that the resilientpinching of the brick by the prongs 40 and 43 holds the spacers in placeupon the brick during storage, shipment and construction of the roof.The spacer is simply snapped in place upon the brick. The prongs may ifdesired be roughened to prevent them from slipping off the brick ends.The prong 43 is desirably mitered at 44 at the corners of the brick.

4Figures '7 and 8 illustrate a. spacer 45 for use between the rear facesof the brick. It corresponds generally in size with the rear face 22 ofthe brick. Figures 9 and 10 show a spacer 46 of the same general size asthe spacer 45, for use between the front faces 2| of the brick. Thespacer 46 is cut away at 41 to permit ready insertion of the hanger 2B.Figures Il and I2 show a spacer 48 for use between the side faces of thebrick.

In the form of Figures l to-3, the spacers will be differently appliedto the bricks of different longitudinalrows, the bricks of one rowcarrying a front face spacer and a left side spacer, while those ofanother row carry a rear face spacer and a right side spacer, forexample.

It will be evident that the sizes and contours of the spacers willdepend very largely upon the sizes and contours of the faces of thebrick, and that, while it isydesirable to have the spacers conform moreor less exactly to the external outlines of the brick faces, the spacersmay, if desired, differ from the external outlines of the brick faces.

It will also be evident that, while Figures 1 and 2 show spacers incontact with all four lateral faces of the bricks (with the exception ofthose bricks at the outer edges of the roof) some advantage rnay beobtained by using spacers between some but not all of the adjoiningfaces of the brick.

Figure 6 shows spacers between the front and rear faces4 2i and 22 butnot between the side faces 23 of the brick.

The hanger and spacer function may be combined in a single fitting, thedetail of which is not important from the standpoint of the presentVimperfectly upon the drawings. The portions of the spacers above thelower ends 49, as for example at 50, are partially converted into oxide,

with correspondingly less, but nevertheless marked, increase in volume.The upper portions of the spacers at 5l have not yet become veryextensively oxidized. The effect of the oxidation upon the suspendedroof has been to ll any slight free space between the bricks left at thetime the roof was constructed, to compensate for the shrinkage whichoccurs in the brick, to exert a lateral force between adjoining bricksand to chemically react with the( adjoining brick welding one brick toanother by a highly refractory and very strong compound, thus producinga 'monolithic construction. Under the pressures developed, some of theiron oxide appears to penetrate small roughnesses in the brick surface.In

kil

the great majority of the cases, all leakage openings-between the brickare'sealed by the growth of the spacers.

The bricks are held so firmly against lateral movement after the spacersoxidize that an individual brick may even break in pieces, and yet thepieces will not fall out. This is particularly important in the case offurnaces which are shut down from time to time, with the resultanttremendousI ,expansions and contractions. The spacers serve to seal theroof against leakage of combustion gases `or entrance of air into thefurnace, thus improving the heat efciency and prolonging the life of thefurnace.

When the roof is firsty subjected to furnace temperature, the respectivebrick and spacers are relatively loose andfree to move and to readjustas required by the pressure on the individual partsof the construction.Readjustment during the initial heating up of the roof is very desirableto prevent localized abnormal stresses upon individual bricks. It isonly after the roof has been thoroughly heated at furnace temperature,and the action of the oxidizing atmosphere of the furnace has caused thespacers to oxidize, that the individual bricks are integrated together.

The spacers must not collapse nor compress laterally under pressure, asif they do so, they cannot by increase in volume exert lateral pressureon the bricks. Therefore each spacer should 'preferably comprise asingle thickness of metal.

In order to indicate that various forms of brick may be used, Figures 13and 14 show a different type of brick 20 having a recess 21 in which anysuitable hanger may be inserted, and provided with spacers 52. Manyvariations of hangers may be used, and it is not desired to conne thepresent invention to constructions showing any particular type ofhanger.

The brick employed in the present invention has the desirable propertiesof prior art chrome brick without some of the disadvantages of suchprior' art chrome brick. The novel brick is manufacv chrome particlesand using instead smaller magi tured by employing the principle ofgrading the size of larger and smaller particleswhile omittingintermediate sized particlesv as previously discussed by the presentinventor, and in addition, rejecting'some or preferably all of thesmaller Anesia particles. The use of smaller magnesia pare ticles inpreference to smaller chrome particles in a brick chiefly containingchrome ore increases theresistance to spalling; to crushing, to hightemperatures and to basic slags and the volume stability beyond theproperties of chrome brick of the prior art, without serious loss indensity or increase in porosity.

Chrome is a satisfactory basic refractoryv for many purposes because ofthe great strength,

hardness, resistance to crushing and volume stability of its particlesand theirchemicalinertness in the metallurgical furnace. Atypiml-v-'analysis of chrome ore used for refractory purposes is herefrom 100.00

a volume stable skeleton or matrix in the brick.4

It is important to use chrome ore rather than magnesia as the majorconstituent of this matrix since magnesia exhibits an excessiveshrinkage at the temperatures cf an open hearth steel furnace, forexample, The larger chrome particles are supplemented with additions ofsmaller particles of-magnesia. The magnesia particles serve as a coatingupon the chrome particles, bonding the chrome particles, protecting thechrome so as to make the brick more resistant to iron oxide and anyother basic oxides and reacting readily with the iron oxide of thespacer. In this Way the objectionable properties of chrome ore, such asits poor bonding qualities, its lack of resistance to iron oxide aridother basic oxides and its lack of vigorous reactivity with the ironoxide of the spacer, are overcome and objectionable features ofmagnesia, such as its tendency to shrink excessively at the temperatureof the open hearthA steel furnace, are also not harmful.

For the smaller particles magnesia which is desirably the calcined ordead-burned magnesite or periclase of ,usual commercial grade is em'-pl'oyed. Typical analyses follow:

Percent Percent Ignition loss 0.00 0. 10 Silica 0. 67 3. 36 Ferrieoxide. 7. 13 1.46 Alumina. 0. 25 1.02 L1me 2. 29 1.11 Magnesia bydliierenc 89. 66 92. 95

'rtm1 10o. oo 10o. oc

These analyses are, of course, subject to variation within the usualIcommercial range, and

and 20 mesh per linear inch, and may very desirably be more closelygraded as to size, for ex,

ample ranging between-6 and 20 mesh per linear inch, between 3 and 10mesh per linear inch, or

be 3 and 6 mesh per linear inch, etc.

urse it will be understood that no commuch as 10% or even in an extremecase 15% in the dry mix, o1 chrome particles of smaller size. Likewise,there may-be a small proportion, possibly 1% or 2% or even in an extremecase 5% in the dry mix, of chrome particles 'of-larger size.

screening process is one hundred per cent eilicient and that,notwithstanding due care,

vbrick which is suitable for use withoutprevious Based on the weight ofthe refractory, there may be as much as 15% of the larger particlesoutside the chosen size rangedue to the inefdciency of commercialscreening. 'Ihis will be made clear by the following typical screenanalyses of chrome particles commercially graded to be between 6 and 20mesh per linear in'ch in one case, between 3 and 10 mesh per linear inchin another case, and between 3 and 6 mesh per linear inch in anothercase:

Mesh per linear inch 6 x 20 3 x 10 3 x 6 Percent Percent Percent On 3Nil 2 Through 3 on 4 Nil 13 36 Through 4 on 6.--- l 2T .56 Through 6 on8.--. 23 29 4 Through 8 on 10 26 18 2 Through l on 14-- 26 7 Nil Through14 on 20 2l 5 Nil Through 20 3 Nil Nil Total 100 100 l0() Theintermediate size-particles are omitted or thequantity of intermediatesized particles is maintained very low.

The magnesia smaller particles should pass 48 mesh per linear-inch. Theyhave the following typical screen analysis:

Mesh per linear inch- It will of course be evident that the illneness of1f' the smaller particles may be increased, using smaller -particles forexample passing entirely through 65 mesh per linear inch,'or evensmaller.

Of the chrome larger particles, between 65% and '75% (that is, between65 and '75 parts in 100 parts) are employed, preferably using about'70%.

Of the magnesia smaller particles, between 35% and 25% (between 35 and25 parts in 100 parts) are employed, preferably using about 30%.

To a slight extent chrome may be substituted for magnesia and magnesiafor chrome without aiecting the special properties of the brick,although the larger particles will be chiefly or predominantly chromeand the smaller particles chieily or predominantly magnesia. This meansthat more than 50%, most desirablyv100%, of the larger particles will bechrome ore, and more than 50%, most desirably 100% of the smallerparticles will be magnesia. The larger particles will preferablycomprise in excess of 80% chrome and not over 20% magnesia, while thesmaller -particles will preferably comprise in excess of 80% magnesiaand not over 20% chrome. This will be understood when reference ismadein the claims to larger particles of chrome and smaller particles ofmagnesia.

Conventional brick-making practice is used as far as the preparation ofthe brick mix is concerned. 'Ihe larger chrome particles and smallermagnesia particles are mixed with water, preferably adding enough waterto temper the mix, desirably about 2% based on the weight of the wetmix. A

Where the brick is'to be kiln fired as later explained, it is notnecessary to use a bonding substance. If it is preferred, however, tomake a kiln firing, a bonding substance should be employed.

As a bonding substance, sulphuric acid may be used. One suitable mixmight be bonded with about 1% of 66 Baum sulphuric acid based" upon theweight of the wet mix (the percentage is practically the same if basedon the dry iinished brick). As much as 2% or even more of sulphuric acidmay be used. Where sulphuric acidof another strength is used,l allowanceshould be made in the percentage employed. For some uses clay may beadded as a bond, and as much as 2% or less desirably even 5%of clay maybe added'if desired in addition to the sulphuric acid.

Other bonding substances such as\sodium acid sulphate, sodium silicateororganic bonding substances like waste .liquorslfrom the sulphite paperprocess, dextrin, etc., may be used. 'I'he quantity of sodium acidsulphate, sodium silicate or organic bonding substance will mostdesirably be limited to 1% or permissibly 2% of the wet mix, notconsidering in this 2% the water which is used to dissolve the bondingsubstance. In any case the quantity of any such bonding substance willnot exceed 5% of the wet mix. Clay, preferably not exceeding 2% but lessdesirably up to 5% of the wet mix, maybe used with any of the abovebonding substances.

The total bonding substance will very desirably be limited to 5% of thewet mix so as not to impair the refractory properties of the brick. Thebonding substance may be mixed with the tempering water beforeincorporating the water in the mix. l

The molstened brick mix is molded under a pressure exceeding 1000 poundsper square inch (70.3 kilograms per square centimeter), preferablyexceeding 5000 pounds per square inch (351.5 kilograms per -squarecentimeter), and most desirably exceeding 10,000 pounds per square inch(703 kilograms per square centimeter). It is preferable to apply aVacuum during the molding, increasing the pressure in a second stepafter the vacuum is applied.

The molded brick, if they are to be kiln fired, are dried preparatory tokiln ring, and then fired, suitably at a temperature such as 1830" F.(1000 C.) or above, for example 2190 F. (1200 C.) or 2730 F. (1500 C.).Where a bonding substance has been used, the brick need not be kiln red,but should be treated to develop the bond, after which they may beshipped-in unburned condition and subjected to firing temperature forthe first time in the metallurgical or chemical furnace in which theyare used. The preferred treatment to develop the bond is to heat themoist brick to a temperature between.

212 and 572 F. (100 and 300 C.) until 1Sub-- stantially all freemoisture is removed. The dry invention when bonded and in unflredco'ndition,

after drying for.75 hours at'25'l F. (125 C.) has a bulk specificgravity in excess of 3.10, preferably about 3.20. The open pore space isless than 10%.

A very high resistance to spalling is obtained in the actual finishedbrick as indicated by tests under conditions of 'actual use. -The coldcrushing strength of the dry unred brick exceeds 2000 pounds per squareinch (140.5 kilograms per square centimeter) and often exceeds 4,000pounds per square inch (281 kilograms'per square centimeter). Y

'I'he brick of the present invention in unilred condition is very volumestable and has excellent resistance to high temperature, as indicated bythe fact that when rcheated in a testing furnace to 3300 F. (1815 C.)for 24 lhours or more the brick show a change in linear dimensions ofless than 1% shrinkage.

Tests undr actual conditions of use indicate very high resistance tobasic slags and other basic oxides.'

The eiliciency of the sulphurio acid bond depends of course upon thepresence of magnesia smaller particles and `is slightly diminished bysubstitution of chrome smaller particles for magnesia. 'I'he bond, afterit is once developed, is effective at ordinary room temperatures land issupplemented after the brick are heated to firing temperature duringuse, by a reaction between the constituents of the brick. The excellentservice characteristics of the brick of the present invention, andparticularly the resistance to spalling, crushing, high temperatures andbasic slags, and the volume stability, are due in part to the tightintertting between particles, to the presence of an optimum size ofchrome particles, to

the presence of the magnesia smaller particles.

and to the presence of 'an optimum proportion and optimum size ofmagnesia particles.

The magnesia in the brick is important not only from. the standpoint ofthe properties of the brick itself, but also in order to render thebrick capable of reacting readily with the oxide of the spacer metal tounite the brick firmly to the spacer by a compound which is refractoryand volume stable under the furnace conditions and which makes of theroof effectively a monolithic structure.

Where reference is made to a sulphate acid bonding substance it isintended to include both sulphuric acid and acid sulphates such assodium acid sulphate.

The screens which have been described as possessing certain mesh perlinear inch are Tyler Standard screens.'

Commercial Ascreening frequently employs screens which are inclined atan angle from the horizontal and have rectangular openings. Thesescreens should be chosen so that the particles which -are produced, whentested by screening over standard screens, shall conform to the requiredgrading.

'. All percentages mentioned herein arepercentotal material beinganalyzed.

Percentages based upon the dry mix are substantially identical forpractical purposes with percentages based upon the dry nnished brick,

and one can be used as the other without change 1f desired. i

In view of my invention and disclosure variations and modifications tomeet individual whim or particular need will doubtless become evident toothers skilled in the art, to obtain au or part.

of the benefits of my invention without copying the structure shown, andI, therefore, claim all such in so far as they fall within thereasonable spirit and scope of my invention.

Having thus described my invention, Whatl claim' as new and desire tosecure by Letters Patent is:

l. In a refractory roof, a plurality of suspended refractory brickspositioned side by side, supported by hanging from above, having lateralfaces which are adjacent and generally parallel and comprising chieychrome ore with mag- 'nesia as the chief minor constituertkand spacersbetween lateral faces of the bricks, each spacer contacting therefractory material of the generally parallel faces of adjacent bricks,the spacers comprising iron part atleast of which is oxidized and ironoxide of the spacers being combined with the magnesia of the bricks onboth sides of individual spacers.

2. In a refractory roof, a plurality of suspended -refractorybrickspositioned side by side, supported by hanging from above, having lateralfaces which are adjacent and generally parallel and comprising chieflychrome ore in the form `of relatively larger particles with magnesia in*the form of relatively srrialler particles interspersed among and coatedon the larger chrome particles, and spacers between the lateral faces ofthe bricks, each spacer. contacting the refractory material of thegenerally parallel faces of adjacent bricks, the spacers comprising ironpart at least of which is oxidized and iron oxide of thev spacers beingcombined with the magnesia. of the bricks on both sides of individualspacers."

3. An open hearth steel furnace roof having a plurality of volume-stablechrome-magnesia suspended refractory bricks positioned side by side,supported by'hanging from above, having lateral faces which 'areadjacent and generally parallel and containing more than 50% chrome ore,yand chrome ore with magnesia as the chief minor constituent, means forindividually hanging the bricks from above and spacers between lateralfaces of the bricks, each spacer contacting the refractory material ofthe generally parallel faces of adjacent bricks, the spacers comprisingiron part at least of which is oxidized and iron oxide `of the spacersbeing combined with the magnesia of the bricks on both sides ofindividual spacers. 5. In a suspended refractory roof, a plurality ofdry chrome-magnesia suspended refractory bricks positioned side by side,supported by hanging from above, having lateral faces which are adjacentand generally parallel and comprising 75 tightly intertted masses offrom 65 to '75 partsof larger particles consisting chiey of chrome oreand large enough to be retained 0n a 20 mesh per linear inch screen andfrom 35 to 25 parts of smaller particles consisting chieiiy of mag'-nes'ia and small enough to pass through a. 48 mesh per linear inchscreen in combination with spacers between the lateral faces` of thebricks,

each spacer contacting the refractory material of the generally parallelfaces of adjacent bricks, the spacers comprising iron part at least ofwhich is oxidized and the iron oxide of the spacers being combined withthe magnesia of the bricks on both 5 sides of individual spacers.

RUSSELL PEARCE HEUER.

